Power over ethernet management devices and connection between ethernet devices

ABSTRACT

In one embodiment, a connection is maintained between a pair of ethernet ports that have circuitry connected in series with the ports and receiving power-over-ethernet (PoE) from one of the ports, by providing a controllable bypass circuit coupled to the pair of ethernet ports in parallel with the circuitry receiving power-over-ethernet, sensing a preselected condition, and opening and closing the bypass circuit in response to the presence or absence of the preselected condition. Power sourcing equipment (PSE) may supply the one of the ports with power over ethernet, and the circuitry may transports data between the pair of ethernet ports. The circuitry may also supply the switch with a control signal in response to the detection of the preselected condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Ser.No. 60/674,684 filed Apr. 26, 2005.

FIELD OF THE INVENTION

This invention relates to Ethernet management devices used in thedelivery of “paid for” Ethernet services by telecommunication carriersand operators, or by other organizations.

BACKGROUND OF THE INVENTION

The IEEE 802.3af standard defines a mechanism to deliver power to anEthernet device via the Ethernet wire, known as “Power Over Ethernet” orPoE. FIG. 1 depicts a typical IEEE 802.3af setup in which power isdelivered to a powered device (“PD”) 10 (right side Ethernet device)from a power sourcing equipment (“PSE”) 11 over a category 5 Ethernetcable 12. The power delivery may be using the data copper wire pairs(mode A) or the unused copper wire pairs (mode B). The left sideEthernet device 11 is not powered by PoE; it draws power from anothersource. It is the PSE device 11 that decides which wires to use (mode Aor mode B). A typical mid-span injector (where the PSE 11 a is separatefrom the Ethernet device 11 b) usually uses mode B, while a device thatembeds a PSE typically uses mode A.

SUMMARY OF THE INVENTION

In one embodiment, a connection is maintained between a pair of ethernetports that have circuitry connected in series with the ports andreceiving power-over-ethernet (PoE) from one of the ports, by providinga controllable bypass circuit coupled to the pair of ethernet ports inparallel with the circuitry receiving power-over-ethernet, sensing apreselected condition, and opening and closing the bypass circuit inresponse to the presence or absence of the preselected condition. Powersourcing equipment (PSE) may supply the one of the ports with power overethernet, and the circuitry may transports data between the pair ofethernet ports. The circuitry may also supply the switch with a controlsignal in response to the detection of the preselected condition. In onespecific implementation, the switch comprises a pair of double-throw,double-pole relays having coils energized by power over ethernet, andtwo pairs of contacts for (a) opening the bypass circuit to couple thepair of ethernet ports via the circuitry and (b) connecting the ethernetports to the circuitry, in response to energization of the relay coils,and for (a) closing the bypass circuit to couple the pair of ethernetports directly and (b) disconnecting the circuitry from the ethernetports, in response to de-energization of the relay coils.

In another embodiment, an ethernet link includes an ethernet managementdevice that does not terminate the link, power sourcing equipment forsupplying power over ethernet to the device, and a powered device,within the ethernet management device, receiving power over ethernetfrom the power sourcing equipment and powering the ethernet managementdevice. The ethernet management device may be a repeater. The ethernetlink may couple an operator's network and a customer's network, and theethernet management device may provide a management function for thecustomer's network.

In another embodiment, an ethernet link includes first power sourcingequipment for supplying power over ethernet to at least one powereddevice, and a repeater or relay located between and coupled to the firstpower sourcing equipment and the powered device. The repeater or relayreceives and supplies power over ethernet from the first power sourcingequipment via four pairs of conductors including both data signalconductor pairs and unused conductor pairs. The repeater or relay mayinclude internal powered devices receiving power over ethernet from thefirst power sourcing equipment, and second power sourcing equipmentsupplying power over ethernet to the at least one powered device coupledto the repeater or relay. The internal powered devices may supply powerto the second power sourcing equipment, which in turn may supply powerover ethernet to the powered device or devices connected to the repeateror relay.

In another embodiment, a network device having at least first, secondand third ethernet ports includes circuitry connected in series with thefirst and second, and with the first and third, ethernet ports andadapted to receive power-over-ethernet (PoE) from the first port viaeither two pairs of data signal wires or two pairs of unused wires; abypass circuit coupled to the first and second ethernet ports, via thetwo pairs of unused wires, in parallel with the circuitry receivingpower-over-ethernet from the first port; and a switch for closing thebypass circuit in response to the supplying of power to the circuitryvia the data wires. A VoIP telephone may be coupled to the second port,and a LAN may be coupled to the third port.

In another embodiment, a pair of ethernet devices are coupled to eachother through at least one repeater and adapted to communicate with eachother using an administrative protocol that defines messages used toexchange information or commands. The repeater includes a controllerprogrammed to communicate with at least one of the ethernet devicesusing the administrative protocol, including a MAC address for therepeater. The administrative protocol may be the OAM protocol defined byclause 57 of IEEE 802.3ah, modified to allow MAC-level addressingbetween an Ethernet device and a repeater, to carry OAM information.

In another embodiment, an ethernet includes a physical ethernet segmentshared by at least two protected private networks coupled to a carriernetwork, a first special client coupled to the interface between theethernet segment and one of the protected private networks, a secondspecial client coupled to the interface between the ethernet segment andthe other of the protected private networks, and a network resolverbetween the ethernet segment and the carrier network. Each of thespecial clients and the resolver have a unique MAC address and isprogrammed to find the MAC address corresponding to an IP address, eachof the special clients is programmed to send an ARP request to thenetwork resolver using a unicast destination address, and the networkresolver is programmed to respond to the request using a unicast ARPreply.

In another embodiment, a network device having a pair of ethernet portsincludes circuitry connected in series with the ethernet ports fordetecting incompatibility of ethernet devices coupled to the ethernetports and correcting any detected incompatibility, a bypass circuitcoupled to the pair of ethernet ports in parallel with the circuitry forcoupling the ports, a sensing element responsive to a preselectedcondition, and a switch responsive to the sensing element for openingand closing the bypass circuit. The incompatibility may be detected bydetermining the link partner capability of the link partner at each ofthe ports, and then comparing the capabilities to detect anyincompatibility.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a power over ethernet system of the type definedby the IEEE 802.3af standard;

FIG. 2 is a block diagram of a device connected to a power over ethernetsystem and providing a fail over bypass;

FIG. 3 is a block diagram of one implementation of the deviceillustrated in FIG. 2;

FIGS. 4 and 5 are diagrammatic illustrations of the relay circuit in theimplementation of FIG. 3;

FIG. 6 is a flow chart of a routine executed by the CPU in theimplementation of FIG. 3

FIG. 7 is a block diagram of a managed ethernet service;

FIG. 8 is a block diagram of the ethernet management device in thesystem of FIG. 7;

FIG. 9 is a diagrammatic illustration of the POE+ extension to the IEEE802.3af standard;

FIG. 10 is a diagram of a system having a repeater or relay locatedbetween the power source and the powered devices of FIG. 9;

FIG. 11 is a block diagram of one implementation of the repeater/relayof FIG. 10;

FIG. 12 is a flow chart of an algorithm executed by the implementationof FIG. 11;

FIG. 13 is a block diagram of an ethernet management device thatprovides power to two devices at the same time;

FIG. 14 is a flow chart of a routine executed by the device of FIG. 13;

FIG. 15 is a diagrammatic illustration of two ethernet devices coupledthrough a series of repeaters;

FIG. 16 is a flow chart of a routine executed by the repeaters of FIG.15;

FIG. 17 is a pair of flow charts illustrating the operation of theethernet devices of FIG. 15 with regard to a particular type of traffic;

FIG. 18 is a diagrammatic illustration of two private networks sharingthe same physical ethernet segment;

FIG. 19 is a flow chart of a routine executed by the special clients inthe system of FIG. 18;

FIGS. 20-23 are flow charts of routines executed by the network resolverin the system of FIG. 18;

FIG. 24 is a block diagram of an ethernet device connected between twoethernet devices and providing a fail over bypass;

FIG. 25 is a flow chart of a routine executed by the device of FIG. 24;and

FIG. 26 is a pair of diagrammatic illustrations of two types ofconnections in the bypass circuit in FIG. 24.

POE AND FAIL OVER BYPASS

One aspect of the invention, illustrated in FIG. 2, is to provide adevice 20 having at least two Ethernet ports 21 and 22 with thecapability of allowing the two ports to be electrically connected in theevent of a failure (using an electrical bypass 23), including, but notlimited to, a power loss, while keeping the capability of being poweredby a PoE PSE 24 (once power comes back) using the IEEE 802.3af standard(PoE). Only one of the Ethernet ports 21 and 22 is a PoE client (calledthe PD).

Having a fail over bypass mode is particularly useful in situationswhere high availability of an Ethernet connection is important. Thedevice's failure or power failure will not impair this highavailability. But at the same time, being able to be powered even whenin bypass mode is important for the device to resume its duty when thefault condition is corrected. A simple example is when the failure is apower outage; it would be desirable to re-power and restart the devicewhen power is back.

All of the normal features of PoE, including detection andclassification, should be supported and should not be affected in anyway by any type of circuit on the non-PD port.

The device 20 is in normal operation when the bypass 23 is disabled andthe two external Ethernet devices are connected to the Rest of Circuit25. Power injected by the injector 24 feeds the device 20. In bypassmode, the Ethernet signal directly connects the two Ethernet devices,bypassing the Rest of Circuit 25, but the injector is still capable ofpowering the device 20.

In an implementation of the device 20 illustrated in FIG. 3, theEthernet signals are made of two differential pairs in the case ofEthernet and Fast Ethernet, or four differential pairs for GigabitEthernet, but are only shown, for simplicity, as a single wire. Each ofthe ports 21 and 22 includes an RJ45 socket 30 or 31 and an Ethernettransformer 32 or 33 connected to the common contact 50 of a relay 34 or35. In fault mode, the relays 34 and 35 connect in pair (one pair perwire) together and the Ethernet signals pass from one RJ45 connector tothe other via the Ethernet transformers 32 and 33 and the relays 34 and35, using contact 51. In normal mode, the same signals will pass fromone RJ45 connector to the Ethernet PHY 39 and 40 via the relays 34 and35 by using contact 52. Power is blocked by the transformer 32 and issent to a PoE circuit 36. A CPU 37 executes the flow chart of FIG. 6described below. Signals supplied to the CPU 37 from the Rest of Circuit38 on fault flag lines 39 represent the fault reporting statuses thatare used by the CPU 37 to detect the failures and initiate a bypass modeof operation. These lines 39 may be actual electronic circuit(s) or maybe statuses available to the software running on the CPU 37 by readingstatus registers or by other means. The number of such flags depends onthe number of types faults that it is desired to monitor. CPU 37supplies a control signal to the relays 34 and 35 via line 41. The Restof Circuit 38 is connected to the relays 34 and 35 via parallel paths 39and 40 in the physical layer (PHY) of the Ethernet.

The PoE 36 circuit is able to perform as a normal PD and feeds power thedevice 20, as per the IEEE 802.3af standard.

The Rest of Circuit 38 is made of all of the circuit an Ethernet devicenormally has and typically includes a CPU, memory, MAC circuit, etc.There is no special requirement for this circuit. The CPU 37 includeseverything required to decide when to enable the bypass and when not toenable the bypass. Depending to the application, this circuit maysupport different failure modes for the decision process. In the mostcomplete situation, the circuit may need a CPU 37, which may or may notbe a CPU (if present) included in the Rest of Circuit 38, in order toperform the decision.

Various failure modes may trigger the bypass mode. A non-exclusive listis:

-   -   Total power failure    -   Software not running    -   Software detected PHY error or malfunction    -   Software detected error or malfunction in various part of the        rest of circuit, including, but not limited to:        -   Memory error        -   MAC error        -   Partial power supply failure

The CPU 37, controlling relays 34 and 35 via line 41 is designed so thatin the absence of power, the relays position defaults to bypass mode.Once power is applied, the design also maintains the bypass mode untilthe software decides to turn off the bypass mode. The flow chart in FIG.6 illustrates the routine executed by the CPU 37 and includes thefollowing stages.

-   -   Stage 100: this is the un-powered state. The relays are in        bypass mode.    -   Stage 101: power was applied to the device; the software starts        its boot process; the relays remains in bypass mode.    -   Stage 102: the software verifies everything and checks for        failure. The failures may be detected by inspection of an        hardware signal (for ex.: partial power failure), by a memory        test, by a status reported in a register (for ex.: in a phy        register) or by any other means that are deem to be valid        failure indicators. If a failure is detected, the next stage        will be 103, if not then the next stage is 104.    -   Stage 103: the software stops the boot process. The relays        remains in bypass mode.    -   Stage 104: the software turns the relays in normal, none bypass        mode.    -   Stage 105: software boot process is now completed; the software        will continuously monitor everything and check for failure. If a        failure is detected, the next stage will be 106.    -   Stage 106: the relays are put into bypass mode by the software.    -   Stage 107: everything stop, the device is in fail over mode with        the relays in bypass mode.        PoE Powered Repeater or Relay Device

The IEEE 802.3af standard, defining the “Power Over Ethernet” (PoE)function, was created to power “terminal” devices, such as VoIPtelephones, surveillance cameras and WiFI access points.

The diagram in FIG. 7 depicts a typical managed Ethernet service. TheEthernet management device 60 is used to monitor, provision andadminister the service at a point of demarcation, and does not terminatethe Ethernet link. It is located near the point of need, i.e., nearnetwork 61. This is typically used by, but not limited to, a telecomoperator's service offering. Large enterprises or campuses may also usethe same model.

Network 62 represents the operator's network, which may have anyarbitrary topology and technology. It represents a transport system. Itis the primary network, where management systems are located. The powerinjector 63 may be a mid-span injector or an Ethernet device, such as aswitch, router, transport gateway, etc. The network side 64 of theinjector need not be Ethernet; any type of uplink is applicable. Network61 represents the customer's network. An optional Ethernet repeater 65may be present. However, in order to deliver power to the Ethernetmanagement device 60, the repeater implements another aspect of thisinvention described below. It is the delivery of the Ethernet service tonetwork 61 that is being managed.

The Ethernet management device 60 is a complete apparatus that includesa network interface device (NID) 66, two RJ45 ports 67 and 68, and a PD69. The main function of the NID 66 is to relay network traffic betweenthe two RJ45 ports 67 and 68, and is perceived by the network as a layerone device. The PD 69 delivers power to the device 60. Two RJ45 ports 67and 68 represent the Ethernet ports and include Ethernet connectors.

IEEE802.3af is used to power the Ethernet management device 60 (and theinline repeaters 65, if any), which implements the functions of a fullycompliant PD (Powered Device) 69.

The functions of the PD 69 may be implemented in the management device60 by using a commercially available PoE circuit or by designing adiscrete solution using standard components. The design of themanagement device 60 limits the power consumed by the complete unit tothe limit set forth by IEEE 802.3af, i.e., 12.95 W. The power supplydesign, converting the −48V to the voltage(s) used by the device, mustprovide a galvanic isolation between the Ethernet cable's wire and therest of the circuit of the device, including the metal casing (if any).Special attention must be paid to maintain the isolation between the twoRJ45 ports 67 and 68 and their signals.

As required by the standard, IEEE 802.3af, the circuit must be capableof being powered by either the data signals or the unused signals.

By combining an IEEE 802.3af PD function 69 inside the management device60, a more reliable service may be deployed. The delivery of theEthernet service then becomes fully visible (by the management functionof the device) at all times (by the fact that it is powered by theoperator, using PoE) independently of the availability or reliability ofpower at the point of demarcation. Some of the benefits of creating andusing this combination are:

-   -   Extend the reach of Ethernet by using line powered repeaters.    -   No dependency on customer provided UPS power (Uninterrupted        Power Supply).    -   More reliable than AC power (injector may be battery backed-up        and maintained by the operator) and therefore creates a more        reliable service.    -   Better service availability (service is available and monitored        even when no power is present).    -   No power-related false alarms (customer may accidentally remove        the power of the management unit if power is locally fed), thus        reducing operation costs associated to fault or alarm analyses.    -   Allows the operator/carrier to have full responsibility and        accountability for powering the network devices up to the point        of need (agreed demarcation point) and to sell this as a        valued-added service to their customer, providing more revenue.        PoE in a Repeater or Relay with Power Carry Forward

The IEEE 802.3af standard adds powering capability to an Ethernet link.Power is added to the data signal wire pairs or to the unused wirepairs. An extension was made to the IEEE standard to allow adding powerto both the data signal wire pairs and to the unused wire pairs at thesame time, allowing more power to be delivered to the load. In suchcase, detection, classification and monitoring are performedindependently for both power paths. The extension is called POE+ and isillustrated in FIG. 9.

Referring to FIG. 9, a power source 81 includes two items of powersourcing equipment (PSE) 83 and 85, and a unique logical load 82includes two powered devices (PD) 84 and 86. The two PDs 84 and 86 arefully independent from the point of view of the power source 81, whichis connected to the load 82 via a category 5 Ethernet cable 80, withdata signal wires 1, 2, 3 and 6 connecting PSE 83 to PD 84, and unusedwires 4, 5, 7 and 8 connecting PSE 85 to PD 86.

In FIG. 10, an Ethernet repeater/relay 91 is located between the powersource 81 and the load 82. The power handling circuit of therepeater/relay 91 is powered via the Ethernet cable 80, while stillproviding power to the terminating load 82. One of the functions of therepeater/relay 91 is to extend the reach between the two ends of theEthernet link. Extending the reach of the DC power from the power source81 to the load 82 means that there will be more power losses in thecabling plant. That loss and the fact that the repeater/relay 91 needspower requires that the power source be a POE+ source, i.e., providespower on all of the cat 5 cable 80 wire pairs, thus reducing the totalcable loss. The PDs 84 and 86 in the load 82 are normal IEEE 802.3afdevices, i.e., a device that draws power only on either the data signalwires or the unused wires but must be capable of being powered on eitherpath.

FIG. 11 is a block diagram showing the high level modules that implementthe power handling function of the repeater/relay 91. The Rest ofCircuit 92 includes the actual Ethernet repeater or relay function andthe control circuit that operates the PSEs 93 and 94 based on statusesreceived from the two PDs 95 and 96 via lines 98 and 100 and from thePSE circuits 93 and 94 via lines 97 and 99. A first RJ45 102 connects tothe power source 81, while a second RJ45 101 connects to the load 82.The two PDs 95 and 96 are normal IEEE 802.3af PD circuits with theexception that they are connected to only a single power path, i.e.,either the two pairs of data signal wires or the two pairs of unusedwires (normally, a PD must connect to both power paths and use only oneat a given time). For example, the PD 95 may be connected to the unusedwire pairs 88, while the PD 96 is connected to the data wire pairs 87.The data wire pairs 97 are also connected to the repeater or relayfunction via line 104. Similarly, the PSEs 93 and 95 are normal PSEs asper IEEE 802.3af. The PSE 93 is connected to the unused wire pairs 88,while the PSE 94 is connected to the data wire pairs 87. A 48V powerconverter 105 provides power to the local circuit 92.

Each of the two PDs 95 and 96 is designed such that it functionsproperly, i.e., presents the correct detection signature andclassification signature, even when the other PD is fully delivering48V. This specifically means that the presence of 48V 106 on the localside of the PDs 95 and 96 does not impact the normal behavior of thePDs, which therefore present the correct impedance during the detectionand classification phases. The classification impedance is set torequest maximum power from the power source. Also, the two PDs 95 and 96are designed to provide a reliable status of presence or absence ofpower on their respective power paths using lines 98 and 100. Thecontrol circuit 92 waits for both power paths to deliver power beforeattempting to deliver power to the powered devices 82.

The PSE circuits 93 and 94 report to the control logic 92 the detectionof a remote PD on their respective power paths, its classification, theMPS (Maintain Power Signature) and over current condition, using statuslines 97 and 99. See IEEE 802.3af for details. The control circuit 92 isable to turn on and off each PSE circuit individually, using controllines 97 and 99.

Power may only be applied on a power path if a valid device is detected.To provide power beyond the normal 100 m specified by IEEE 802.3af andalso provide power to the repeater/relay device 91, both power paths 87and 88 are used, to minimize power loss, even if the powered devices 82are regular IEEE 802.3af devices, unless the PD is classified as a lowpower device.

The flow chart in FIG. 12 shows a powered device detection andclassification algorithm for achieving the results described above.Since a legacy IEEE 802.3af PD only implements one detection andclassification circuit, the repeater/relay 91 must alternatively performthe detection and classification on each power path, toggling betweenthe two paths. The algorithm illustrated in FIG. 12 only supports validdetection on both paths, but can be modified to only use one power pathif the PD device 82 is a low power device. The illustrated algorithmincludes the following stages:

-   -   Stage 110: The device waits for both power paths from the power        source to be active.    -   Stage 111: Both PSE circuits are disabled and power is delivered        to the external Powered Device.    -   Stage 112: PSE A is enabled. The circuit performs all the        detection and classification operations as per the standard, but        do not go into power delivering mode. The final result may be a        timeout where no device is detected.    -   Stage 113: the result of the detection and the classification is        recorded. A timeout indicates that no device is connected or        that this specific power path is not handled by the device.    -   Stage 114: PSE A is disabled and PSE B is enabled. A delay of        one second is inserted between the two events. The PSE B circuit        performs all the detection and classification operations as per        the standard but do not go into power delivering mode. The final        result may be a timeout where no device is detected.    -   Stage 115: If either PSE A, as recorded in Stage 113 or PSE B        timed out, as a result of stage 114, i.e., no device detected,        the process is restarted from stage 111.    -   Stage 116: Both PSE circuits are set to unconditionally deliver        power without detection or classification. The circuits monitor        the MPS and over current conditions. If any invalid condition        (no MPS or over current), both PSEs are turned of and the        process restarts from stage 111.

The powered device may be a POE+ device, such as another repeater/relayin line).

PoE with Two Powered Devices (PDS)

There are cases where it is desirable to modify the standard PoE modelthat consists of a PSE powering a single PD over a physical cable link.Some situations require that two devices be powered. An example of sucha situation is where a telecommunication operator is providing dataservices and telephony services on the same Ethernet link. It isdesirable to provide power to a management device located in thecustomer's premises and also power a simple VoIP (Voice Over IP) devicethat provides life line support in case of a power failure. Life linesupport provides emergency call support even in the absence of localpower; the equipment involved must therefore be powered from a reliablesource.

Reliance on the customer to provide power to the devices located in thecustomer's premises is typically not reliable enough, even when batterybacked up, to support life line needs. This limits the deployment ofintegrated services over Ethernet.

An embodiment of one aspect of the invention uses an operator-managedpower source that implements an existing extension of the IEEE 802.3afstandard. Such a source, or injector, provides power to both mode-A andmode-B power paths (mode A is where power is delivered over the Ethernetdata wire pairs, while mode B is where power is delivered on unused wirepairs) and independently performs the device detection, classificationand monitoring for both paths.

The embodiment illustrated in FIG. 13 provides power to two devices atthe same time by a method implemented inside a management device 120.Power is delivered to the management device 120 and to the VoIP device122, each using its own dedicated power path from the same Ethernetcable. A power bypass 125 is provided between a pair of RJ45 connectors123 and 124, and the management device 120 uses only the data wire pairsto draw power.

The power source 121 is part of the operator's Ethernet circuit, whichis a classic Ethernet 10/100 BaseT or Gigabit Ethernet. FIG. 13illustrates only the power function, not the data aspects of thecircuit. The data wires from both RJ45 connectors 123 and 124 (pins 1,2, 3 and 6, depicted by the letter D, corresponding to mode A in thestandard) are connected to the Rest of Circuit 126. The data wires fromthe RJ45 connector 123 are also connected to a PD circuit 132, whichbehaves as a normal IEEE 802.3af-compliant circuit and also indicates tothe “Rest or Circuit” 126 which power path is delivering power to themanagement device (path depicted by D or U from RJ45 A 123), using astatus line 131. The PD circuit 132 delivers power to the managementdevice 120, using a power line 130. The unused wires (pins 4, 5, 7 and8, depicted by the letter U, corresponding to mode B in the standard)are connected the other RJ45 connector 124 via a switch 125, which iscontrolled by the Rest of Circuit 126 via control line 129. The thirdRJ45 connector 127 optionally provides data connectivity to a customerLAN 128, where the data service provided by the operator is delivered.There is no PoE function on this port.

The switch 125 connecting the two RJ45 connectors 123 and 124 includesfour open/close interrupters suitable for Ethernet circuits and iscontrolled by the Rest of Circuit 126 using line 129. The fourinterrupters in the switch 125 are normally open when no power isapplied.

The Rest of Circuit 126 performs its data management service and alsocontrols the switch 125 connecting the U wires between the RJ45connectors 123 and 124, and typically includes memory, CPU, Ethernet MACand Ethernet PHY circuits. There is no special requirement except forthe fact that it must detect the information reported by the PD circuit132 and provide a control signal to the switch 125 via line 129.

In normal operation, the Rest of Circuit 126 obtains its power from thepower source 121 via the data wire pairs (mode A). Power on the unusedwires, flows between the two RJ45 connectors 123 and 124 and feeds powerto the VoIP device 122. Both the Rest of Circuit 126 and VoIP device 122implement the full detection, classification and current limitingfunctions as per IEEE 802.3af. The total cable length between the powersource 121 and VoIP device 122 does not exceed the limit set by thestandard (100m).

The flow diagram in FIG. 14 depicts the operation of the Rest of Circuit126, and includes the following stages:

-   -   Stage 140: Power is applied to the management device. The switch        is open by default.    -   Stage 141: The PD circuit performs its function and reports        which power path is being used to the Rest of Circuit.    -   Stage 142: A decision is made to close the switch if power is        being delivered via the D wires.    -   Stage 143: The switch is closed.    -   Stage 144: This state of the switch remains closed until the        power is removed, in which the process resumes at stage 140. The        switch will then default to its open position.        802.3ah in a Repeater Scheme

The IEEE 802.3ah administrative protocol (OAM) is used between twoEthernet physical peers attached to the same wire link. The protocoldefines messages that are used to exchange information or commands. Itis assumed but not defined that the devices will communicate to the restof world the information so gathered or will be remotely controlled tosend commands (such as a loop back command). The communication method isalso not defined; it could be inline with the Ethernet link or viaanother port.

At the link level, the OAM protocol does not need addressing; thetraffic is always destined to the other link partner.

In FIG. 15, two Ethernet devices 150 and 154 are coupled through aseries of three repeaters 151, 152 and 153, which are simple devicesthat do not have communication capability to the rest of the world; theytransparently repeat the traffic without intervention. It may bedesirable to provide OAM capability on the link between two repeaters,but the OAM information is not accessible since it is not possible totalk to the repeaters. An example is the link between the repeaters 151and 152 where the data collected using the OAM protocol by repeater 152is not available due to the lack of a communication means. On the otherhand, the Ethernet devices 150 and 154 are assumed to have communicationcapability to the rest of the world. They could be PCs, which have auser interface, or routers or switches, which are remotely managed, orother types of networking devices.

To circumvent the lack of direct communication with the repeaters 151,152 and 153, one aspect of the invention provides an OAM link betweeneach repeater 151, 152 and 153 and one or both of the Ethernet devices150 and 154. This means that multiple streams of OAM traffic will existon the Ethernet medium; and thus an addressing scheme is required.

In FIG. 15 only three repeaters 151, 152 and 153 are shown, but there isno limit to the number of repeaters that may be used. The repeaters 151,152 and 153 have at least two ports but may have more. The term“repeater” as used herein includes relays.

The Ethernet devices 150 and 154 in FIG. 15 do not need to be physicallyor directly attached to the Ethernet medium. They may be locatedremotely with a variety of networking gear between them and therepeaters. The networking gear may be “dumb” devices, such as hubs,patch panels, etc., or may be complex transport devices and systems,such as ATM, SONET, etc.

To allow the Ethernet devices 150 and 154 of FIG. 15 to communicate witheach of the repeaters 151, 152 and 153, the OAM protocol defined byclause 57 of IEEE 802.3ah is modified to allow MAC-level addressingbetween an Ethernet device and a repeater (to carry OAM information). Abehavior of the repeater is also defined such that the repeaters arediscovered in sequence, allowing the discovery of the topology. As anexample, starting from the Ethernet device 150, repeater 151 may bediscovered first, then repeater 152 and finally repeater 153. Therepeaters do not have knowledge of the other repeaters; they only knowabout two potential OAM peers, which are the Ethernet devices 150 and154.

The repeaters' behavior with regard to other Ethernet traffic is notaltered; they repeat the traffic, as they would normally do. Also,legacy IEEE 802.3ah OAM traffic is not affected by the repeaters 151,152 and 153, which allows a legacy OAM link to be established betweenthe two Ethernet device 150 and 154.

The repeaters 151, 152 and 153 are made smarter by adding to them an OAMfunction, modified in the following ways:

-   -   1. They have a MAC address.    -   2. They are passive DTE as per IEEE 802.3ah specification. They        implement multiple state machines, one for each port, which are        fully independent.    -   3. They generate OAM traffic compliant to the IEEE 802.3ah,        clause 57, but using unicast MAC addresses (for both the source        and destination address) instead of using the multicast address        specified by the standard.    -   4. The OAM traffic they generate uses their own MAC address in        the source MAC address field.    -   5. They accept OAM traffic that is addressed to their MAC        address.    -   6. They always repeat OAM traffic that is using the mandated        multicast MAC address.    -   7. They ignore OAM traffic that is using the mandated multicast        MAC address.    -   8. For each state machine, they learn the MAC address of the        Ethernet device (150 or 154) doing OAM by looking at packets        that match the IEEE 802.3ah protocol type but where the source        and destination MAC address are unicast MAC addresses and are        equal. This Ethernet device (150 or 154) becomes the OAM link        partner for the port associated to this state machine. This is        the MAC address that their OAM traffic is using as the        destination MAC address. This packet is used as a trigger to        initiate the discovery process. They ignore further reception of        this type of packet until their state machine is returned to the        initial state.    -   9. They react to OAM packets that have unicast MAC addresses in        both the source and destination MAC address fields by using the        regular OAM procedure as described above using the ingress port        as an egress port for the reply.    -   10. Independently for each direction, they block OAM traffic        that is using unicast MAC addresses in the destination field        until their discovery process, corresponding to the egress port,        is complete, i.e., when local_pdu is set to ANY. This allows the        Ethernet devices to discover the repeaters in sequence.    -   11. After local_pdu is set to ANY, they set local_satisfied to        FALSE, Local Stable to 0 and Local Evaluating to 0 when a link        down event is detected on any of their ports. The state machine        is returned to the initial state. They do not use Local Stable        set to 0 and Local Evaluating set to 0 otherwise. This is a        fault propagation mechanism.

The flow chart of FIG. 16 illustrates the operation of the repeaters151, 152 and 153 with regard to traffic that is unicast frames with theprotocol type set to 88-09 (slow protocol, see IEEE 802.3ah, clause57.4.2) and the subtype set to 0x03 (OAM, see IEEE 802.3ah, clause57.4.2). All other traffic is not involved in this flow chart and ishandled by the normal repeater function; this includes traffic with theprotocol type set to 88-09, subtype 0x03, but that is using the mandatedmulticast MAC address. In the flow chart, OAM traffic means traffic thatmatches the description earlier in this paragraph. There is one instanceof the flow chart per port. The flow chart of FIG. 16 includes thefollowing stages:

-   -   Stage 160: This is the initial stage, after power up or after        stage 171. In this stage, the flow of OAM traffic between the        two ports is blocked, the recorded MAC address of the OAM peer        is cleared and the OAM process is disabled.    -   Stage 161: The device waits to receive an OAM frame.    -   Stage 162: The device checks if the source MAC address and        destination MAC address are the same and do not match the MAC        address of the device. If all is true, then the next stage is        163; if not, the next stage is 161.    -   Stage 163: The MAC address from the received frame is recorded.        This is the MAC address that will be used by the OAM process as        the destination MAC address.    -   Stage 164: The OAM process is enabled. This OAM operates the        same as a DTE as described in IEEE 802.ah except that it uses        the recorded MAC address in stage 163 as the destination MAC        address. Specifically, it initiates the Discovery process.    -   Stage 165: Discovery process completion is tested. The discovery        is completed once local_pdu is set to ANY. When this occurs, the        next stage is 166.    -   Stage 166: The forwarding of the OAM traffic received on the        other port is enabled.    -   Stage 167: A check of link of both ports is performed. If any of        the ports becomes down, the state machine will move to stage        168. While staying at this stage, OAM traffic received on the        port covered by this state machine is processed by the OAM        process. Forwarding of OAM traffic received on the other port is        performed.    -   Stage 168: Local stable and local evaluating are set to 0.    -   Stage 169: The state machine waits for at least one OAM frame to        be sent so that the peer receives the new local stable and local        evaluating values.    -   Stage 170: The forwarding of the OAM traffic received on the        other port is disabled.    -   Stage 171: The OAM process is disabled and all states and values        used by the OAM process are reset to their default values. This        is particularly true for the recorded MAC address for the OAM        peer. The next stage is stage 160.

At least one of the Ethernet devices 150 and 154 of FIG. 15 has a“modified mode,” allowing communication and interaction with therepeaters 151, 152 and 153 and a legacy mode allowing interaction with alegacy Ethernet device. In order to allow interaction with the repeaters151, 152 and 153, the OAM implementation in one or both of the Ethernetdevices 150 and 154 is modified in the following ways:

-   -   1. They are active DTE as per the IEEE 802.3ah specification,        except for the legacy mode where they can be active or passive        as configured. Legacy mode may be enabled or disabled        independently of the operations described herein.    -   2. They must implement multiple state machines, one for each        discovered peer device (repeater or Ethernet device).    -   3. The OAM traffic they generate always uses their own MAC        address in the source MAC address field.    -   4. They probe or discover devices on the link using the normal        discovery OAM packet modified to use their own MAC address as a        destination MAC address. The probe can be continuous, using any        period, or can be stopped. The criteria for stopping the probing        process are not specified.    -   5. They react using the normal information OAMPDUs (including        discovery) when they receive a reply from a peer. A state        machine for the newly discovered peer is created. It is assumed        that the peer is compliant by the fact that the destination MAC        address is the address of this Ethernet device. A reply that        uses the mandated multicast address is assumed to be received        from a legacy IEEE 802.3ah device. They learn the MAC address of        the peer by looking at the source MAC address field.    -   6. They generate OAM traffic, other than the probes, using        unicast MAC addresses in the destination MAC address field,        except for the legacy IEEE 802.3ah traffic, where the mandated        multicast address is used and which is limited to only one peer.        The unicast address to use is the MAC address of the peer        discovered during the discovery process.    -   7. They must clear all the state machines and start from the        beginning when any of their peers report Local Stable set to 0        and Local Evaluating set to 0 or when the link goes down.    -   8. They shall not react to Loopback Control OAMPDUs if the OAM        packet is received from a repeater that is using the modified        OAM protocol.    -   9. They should implement one state machine using the unmodified        OAM protocol to handle reply from a peer that is using the        multicast MAC address (which indicates a legacy OAM device).

The flow charts in FIG. 17 illustrate the operation of the Ethernetdevice(s) 150 or 154 with regard to traffic that is unicast frames withthe protocol type set to 88-09 (slow protocol, see IEEE 802.3ah, clause57.4.2) and the subtype set to 0x03 (OAM, see IEEE 802.3ah, clause57.4.2). All other traffic is not involved in these flow charts and maybe handled by the legacy OAM function, if it is OAM traffic; this willuse standard, unmodified IEEE 802.3ah-compliant frames. Specifically, inthese cases, the MAC address used in the destination address field shallbe 01-80-c2-00-00-02. In the flow charts, OAM traffic means traffic thatmatches the description earlier in this paragraph. There is one instanceof the flow charts and associated state machines per OAM peer comparableto repeater 151, 152 or 153 (other than another legacy OAM peer), exceptfor the probe operation. The flow charts in FIG. 17 include thefollowing stages:

-   -   Stage 180: This is the probe process. An OAM discovery frame is        sent using the Ethernet device's MAC address as the destination        MAC address.    -   Stage 181: The device waits for the configured period of time;        after this time, if not other wise stopped, the probe process        resumes to stage 180. If any OAM frame with local stable and        local evaluating are set to 0 or if the link goes down, the        probe process will resume to stage 180.    -   Stage 190: An OAM frame is received. As stated before, this is a        unicast frame.    -   Stage 191: A search in a table of existing state machines is        performed to match the source MAC address (MAC address of the        peer).    -   Stage 192: If no existing peer is found in stage 2010, then the        next stage will be stage 194: if not, it will be stage 193    -   Stage 193: Using the state machine and information related to        the peer found in stage 191, the OAM frame is processed        normally, as per the IEEE 802.3ah standard, except for the        destination MAC address of the reply that will be the device's        own MAC address. The next stage is stage 190.    -   Stage 194: A new state machine is created for the new peer. Its        MAC address, found in the source MAC address of the received OAM        frame, is recorded.        IP Traffic Using Unicast Only on an Ethernet Network

Networks, such as Ethernet, are used to carry information, or traffic,between devices. Very often, the information is only destined to asingle device while, on some occasions, it is required to send theinformation to multiple devices. In order to specify the destination, anaddress (MAC address) is used. This address may be unique (unicast) andbelong to a single device, or it can be generic (multicast) and does notbelong to a specific device. Transmitting devices use multicastaddresses when sending to multiple recipients. The method by which thedevices know which unicast address to use when transmitting someinformation to a specific destination is not part of the Ethernetspecification; it is up to the networking protocols, such as IP, toprovide the mechanism to find the correct address to use.

The IP protocol has its own addressing system. Each device has its ownunique IP address. When carrying IP on an Ethernet network, the IPaddress must be resolved to a MAC address. This means that thetransmitting device must use a mechanism to find the MAC address of thedevice that carries the IP address of the destination. The mechanism,known as the address resolution protocol (ARP), is defined by an IETFstandard: RFC 826. This protocol uses a MAC level multicast to broadcasta request to resolve an IP address to all devices. The device that ownsthe IP address replies with its MAC address to the request originator.There is only one device with the specified IP address on a givennetwork. Furthermore, if that IP address is used between networks, thesame restriction applies between the networks; each device has a uniqueIP address. In public internetworking, such as the Internet, this meansthat the IP address scheme must be globally administered.

FIG. 18 illustrates a system in which two private networks 200 and 206need to share the same physical Ethernet segment 204. This is the casewhen a carrier delivers an Ethernet service to a customer and needs touse IP traffic on the Ethernet segment to reach equipment located on thesegment. If no cooperation exists in administering the IP addresses, anaccidental conflict may occur. At least one of the networks musttherefore implement some mechanism to prevent such conflicts fromoccurring. In FIG. 18, the protected networks 200 and 206 are free touse any IP addresses; they do not perform any address conflictprevention with the legacy network 202 (but should make sure that thereis no conflict within themselves, it is assumed that the protectednetworks 200 and 206 are centrally administered). Typically, theprotected networks 200 and 206 belong to the carrier's customer and areconnected by the service provided by the carrier. The legacy network 202consists of devices that only implement the standards protocols and needto access at least one of the special clients 201 and 205 associatedwith the protected networks 200 and 206, respectively. The legacynetwork 202 will typically be located at the carrier's Network OperatingCenter (NOC). The protected networks 200 and 206 and the legacy network202 are arbitrary; they can be composed of any type and any topology ofEthernet devices, including hosts, bridges and routers.

Mechanisms to avoid IP address conflicts are implemented in a networkresolver 203 and in the special clients 201 and 205 The need for suchmechanisms may be demonstrated by an operator/carrier that provides aprivate link between two sites of a customer. The customer's sites arerepresented by the protected networks 200 and 206, while theoperator/carrier's operation, administration and maintenance system isrepresented by the legacy network 202. The special clients 201 and 205are operator/carrier equipment used in the delivery of service to thecustomer. It is desired to use the IP protocol to access these devicesbut without consuming any network resources, such as VLAN, to isolatethe special clients 201 and 205 from the customer's traffic (so as toeliminate IP address conflict).

The special clients 201 and 205 and the resolver 203 are allowed toresolve an IP address (find the corresponding MAC address) by modifyingthe ARP procedure defined by IETF RFC 826. The resolver 203 may be asoftware implementation inside an existing device or may be a dedicatedhardware device that only provides this function.

Each of the special clients 201 and 205 and the network resolver 203 hasa unique MAC address, which may be a static configuration or obtained byother means. This configuration, in addition to the normal IP settings,provides to the clients 201 and 205 the MAC address or addresses of thenetwork resolver 203 or resolvers. There can be multiple networkresolvers (for redundancy reasons), each with its own unique MACaddress.

The network resolver 203 is a two-port device; one of the ports (labeledP) connects to the network to be protected via the Ethernet segment 204,while the other port (labeled L) connects to the network 202 of legacydevices. Unicast traffic may flow between the two ports, as in a bridge.

The special clients 201 and 205 and the network resolver 203 (on its Pport) do not use multicast and/or broadcast IP packets. The specialclients 201 and 205 resolve IP addresses (find the MAC address owningthe requested IP address), if the address is not already known via aninternal table, by sending a modified ARP request directed to thenetwork resolver 203. Contrary to the regular ARP request, the client201 or 205 uses a unicast destination address instead of the normalEthernet broadcast address. This prevents other devices on the Ethernetsegment 204 from receiving the request. The network resolver 203responds to the client 201 or 205 requests using a unicast ARP reply. Incase of a failure, detected by a timeout, the client 201 or 205 isallowed to try an alternate network resolver. The network resolver 203processes the requests by using a regular ARP request on its L port.

The network resolver 203 blocks and intercepts all multicast andbroadcast IP traffic, on either of its ports. It detects when an ARPrequest is destined to one of the special clients 201 or 205 and replieswith the correct MAC address to the originator of the request. This isdone without sending any traffic to the special client, by using aninternally maintained table of MAC addresses.

Upon power up or reset, the special clients 201 and 205 send dummy ARPrequests to the network resolver 203, using the IP address 0.0.0.0 orthe IP address of the gateway, if one is configured in the client. Theystop sending the requests once they have received a reply, but repeat itafter a programmable inactive period or when their IP address ischanged. The network resolver 203 uses this process to populate itsaddress resolution table.

FIG. 19. is a flow chart of a routine executed by the special clients201 and 205. This routine includes the following stages:

-   -   Stage 210: The special client starts from power up.    -   Stage 211: After initialization, the special client sends dummy        ARP frames, directing them to the resolver. A copy is sent to        all configured resolvers. The requested IP address is either        0.0.0.0 or the IP address of its configured gateway.    -   Stage 212: A reply from the resolver is received. If all        resolvers respond, the routine proceeds to the next stage. If        not, the routine returns to Stage 211, but only for the missing        resolvers.    -   Stage 213: Wait for need to resolve an address. Stage 214: A        modified ARP request is set to the current resolver. The format        of the ARP is the same except that instead of a broadcast it is        a unicast directed to the resolver.    -   Stage 215: A check is performed to detect the reception of a        valid reply.    -   Stage 216: If no reply is received, the routine checks if        another resolver is available.    -   Stage 217: A switch to the other resolver is performed. The next        stage is 214 where an ARP request is sent to the new resolver.    -   Stage 218: A valid ARP reply is received. This is a standard ARP        request, and the standard ARP reply processing is performed.        This includes recording the information requested.

FIGS. 20-23 are flow charts of routines executed by the resolver 203.These flow charts include the following stages:

FIG. 20: Receiving a Unicast Frame on the Legacy Port.

-   -   Stage 220: A unicast frame is received on the legacy (L) port.    -   Stage 221: A check is performed to find if the destination MAC        address matches an entry in an internal table.    -   Stage 222: An entry is found; the frame is forwarded to the        Protected (P) port.    -   Stage 223: No entry is found; the frame is discarded.

FIG. 21: Receiving a Unicast on the Protected Port.

-   -   Stage 230: A unicast frame is received on the Protected (P)        port.    -   Stage 231: A check if performed to detect if the frame is an ARP        request.    -   Stage 232: If the frame is not an ARP, it is forwarded to the        legacy port (L).    -   Stage 233: A check is performed to detect if the frame is a        dummy ARP from a special client.    -   Stage 234: The frame is an ARP request from a special client 201        or 205; it is modified to make it a standard ARP request and        forwarded to the legacy port.    -   Stage 235: The frame is a dummy ARP request; an entry        corresponding to the special client 201 or 205 is created if        none exists, or it is updated if an entry already exists. The        special client 201 or 205 MAC and IP addresses are recorded. A        reply is sent to the special client, using the MAC address of        the resolver in the response.

FIG. 22: Receiving a Broadcast on the Legacy Port.

-   -   Stage 250: A broadcast frame is received on the legacy port.    -   Stage 251: A check is performed to find if the frame is an ARP        request.    -   Stage 252: The frame is an ARP request; a search in an internal        table is performed to find a matching entry for the destination        IP address requested.    -   Stage 253: A matching entry is found if the IP address of the        request matches the IP address of a special client 201 or 205.    -   Stage 254: A standard ARP reply is created, using the        information of the matching special client, and sent to the        requester on the legacy port.    -   Stage 255: The frame is dropped.

FIG. 23: Receiving a Broadcast on the Protected Port.

Stage 240: A broadcast frame is received on the Protected port.

Stage 241: The frame is unconditionally dropped.

Automatic MDI/MDIX Selection Support with Fail Over Bypass

The Ethernet physical layer (IEEE 802.3, clause 14) defines theconnection between two Ethernet devices using twisted pair cabling. Toproperly connect, each device must connect its transmitter to the otherdevice's receiver and vice-versa. In order to do this, the standarddefines a connector pinout (clause 14.5.1, this pinout is called MDI)and a crossover function (clause 14.5.2) that connects each device's TXpins to the other device's RX pins. The crossover function may beimplemented in the cabling or in one of the devices, which changes theTX and RX pin definitions. In the latter case, the pinout is calledMDIX. Also, a device may implement an automatic MDI/MDIX crossoverfunction (IEEE 802.3 clause 40.4.4) that is used to detect the propertype of pinout (MDI or MDIX) required in order to establish an Ethernetlink. Without a crossover function in the cabling, one of the devicesmust implement, or operate as, an MDI pinout while the other must beusing MDIX.

The device 260 of FIG. 24 implements an Ethernet fail over bypass mode,providing an electrical bypass between a pair of ports 263 and 264 undercertain circumstances such as, but not limited to, power failure. Innormal operation mode, the Ethernet connections are routed from eitherport 263 or 264 to the Rest of Circuit 265, which may be any type ofdevice that uses at least two Ethernet ports, such as an Ethernetswitch, a server, a relay, etc.

The Rest of Circuit 265 illustrated in FIG. 24 implements two Ethernetports including Ethernet PHY circuits. In one example, these EthernetPHY circuits implement an automatic MDI/MDIX function, which eases theinstallation by performing an automatic cross over function (IEEE 802.3clause 40.4.4), without worrying about the type of cabling, i.e., withor without crossover.

Since the Rest of Circuit 265 of device 260 implements an automaticMDI/MDIX crossover function, the two external Ethernet devices 261 and262 may be of any type. The cabling 266 and 267 between them and thedevice 260 may or may not have the cross over function. In bypass mode,the connection between the Ethernet device 261 on port A and theEthernet device 262 on port B will fail if both devices are of the sametype (i.e., both are MDI or MDIX), unless one of the devices implementsan automatic MDI/MDIX crossover function or if the cable 266 or 267, butnot both, is a cross over cable.

Implementing the two complementary mechanisms in device 260 assures thatthe bypass mode successfully enables the two Ethernet devices 261 and262 to connect. Not having this feature may defeat the purpose of havinga bypass mode since it is present to assure the connectivity, even inthe case of a malfunctioning device 260, if the cross over is improper.The first mechanism is used to detect the incompatibility byimplementing a detection algorithm. The second mechanism is used tocorrect, if required, the incompatibility.

Detection (while not in Bypass Mode)

In order to detect the incompatibility, the device 260 implements a linkpartner capability detection mechanism. Once the link partner capabilityof each link partner (261 and 262, one for each port) is determined, thetwo results are compared in order to detect the incompatibility. Theroutine illustrated by the flow chart of FIG. 25 includes the linkpartner capability detection mechanism, which is implementedindependently of each port. The routine illustrated in FIG. 25 includesthe following stages:

-   -   Stage 270: The PHY is ser to enable its automatic MDI/MDIX        capability.    -   Stage 271: The device waits for the link to get established.    -   Stage 272: It is assumed that the link partner uses a        configuration opposite to the configuration (MDI or MDIX) used        by the PHY. This configuration setting is recorded.    -   Stage 273: The PHY is set to disable its automatic MDI/MDIX        capability and is set to use the same configuration stored in        stage 272.    -   Stage 274: The device waits for a link to get re-established or        until a timeout occurs. The timeout period is at least as long        as the sample timer defined in IEEE 802.2 clause 40.4.5.2.    -   Stage 275: The outcome of stage 274 is tested.    -   Stage 276: If the link was established, without a timeout, the        recorded value stored in stage 272 is changed to indicate that        the link partner has the automatic MDI/MDIX capability.    -   Stage 277: A timeout occurred, the PHY is set to enable its        automatic MDI/MDIX capability.    -   Stage 278: The device waits for the link to get re-established        or until a timeout occurs. The same timeout period of Stage 274        is used.    -   Stage 279: The outcome of stage 278 is tested. If a timeout        occurred, the next stage is stage 270.    -   Stage 280: The type of link partner is known (MDI, MDIX or        automatic MDI/MDIX capable) and recorded (in stage 272 or 276).        The device waits until the link is broken. When this occurs, the        next stage will be stage 270.

Once both ports have a valid link established and once the type of linkpartner they have is known, i.e., both port's flow charts are at stage270, the detection of incompatibility between the two link partners canbe determined. The following table indicates the result of the detectionmechanism based on the type of link partners detected:

Link partner A Automatic Link partner B MDI MDIX MDI/MDIX MDIIncompatible Compatible Compatible MDIX Compatible IncompatibleCompatible Automatic Compatible Compatible Compatible MDI/MDIX

Once the result of the detection mechanism is known, it may be reportedto an external agent, such as an SNMP trap monitor, or it can be queriedby an external agent, such as an SNMP console, or made available byother means, such as a Web page, etc. Also, in case of incompatible linkpartners, the correction mechanism may be used.

Correction (while in Bypass Mode)

When in bypass mode, the direct connection between the link partners 261and 262 connected to port A and port B of device 260 must implement aselectable crossover function. The selection is used to include orexclude a crossover in the path between the two Ethernet connectors 263and 264 when the bypass mode is active. The correct selection of thiscrossover function is established by the detection mechanism when device260 is not in bypass mode.

In FIG. 26, a cross over path 290 and a straight path 300 are shown.They are part of the bypass circuit 268 of device 260. The completebypass circuit 268 that connects the two Ethernet connectors 263 and 264and the device's Ethernet PHY circuit (included in 265) is not shown.

Since it is necessary for the bypass mode to be valid even when no poweris present, the crossover selection is valid even when such power is notpresent.

A number of methods may be used to implement the selectable cross overmode for the bypass 268 between the two Ethernet ports 263 and 264.Three examples for the selection of the cross over or straight paths areas follows:

1. The cross over vs. straight path selection for the bypass between thetwo Ethernet ports may be implemented by using mechanical switches thatan operator will set to be in cross over mode or not, based on thedetection done by the unit at the installation time.

2. The cross over vs. straight path selection for the bypass between thetwo Ethernet ports may be implemented by using jumpers that an operatorwill set to be in cross over mode or not, based on the detection done bythe unit at the installation time.

3. The cross over vs. straight path selection for the bypass between thetwo Ethernet ports may be implemented by using two DPDT relays suitablefor Ethernet operation. Using this approach, the device may select thecorrect setting based directly on the result of the detection ofincompatibility.

While particular embodiments and applications of the present inventionhave been illustrated and described, it is to be understood that theinvention is not limited to the precise construction and compositionsdisclosed herein and that various modifications, changes, and variationsmay be apparent from the foregoing descriptions without departing fromthe spirit and scope of the invention as defined in the appended claims.

1. A pair of Ethernet devices coupled to each other through at least one repeater and communicating with each other using an administrative protocol that defines messages used to exchange information or commands, said repeater including a controller programmed to communicate with at least one of said Ethernet devices using said administrative protocol, wherein said administrative protocol is an Operation administration and Maintenance (OAM) protocol, modified to allow MAC-level addressing between an Ethernet device and a repeater, to carry OAM information.
 2. The pair of ethernet devices of claim 1 wherein said administrative protocol includes a MAC address for said repeater.
 3. The pair of ethernet devices of claim 1 wherein at least one of said ethernet devices includes a controller programmed to discover multiple repeaters in sequence.
 4. An ethernet comprising a physical ethernet segment shared by at least two protected private networks coupled to a carrier network, comprising a first special client coupled to the interface between said ethernet segment and one of said protected private networks, a second special client coupled to the interface between said ethernet segment and the other of said protected private networks, and a network resolver between said ethernet segment and said carrier network, each of said special clients and said resolver having a unique MAC address and being programmed to find the MAC address corresponding to an IP address, each of said special clients being programmed to send an ARP request to said network resolver using a unicast destination address, and said network resolver being programmed to respond to said request using a unicast ARP reply.
 5. The ethernet of claim 4 wherein said network resolver is programmed to block and intercept multicast and broadcast IP traffic on any of its ports.
 6. The ethernet of claim 5 wherein said network resolver includes an address resolution table of MAC addresses corresponding to IP addresses, and said special clients are programmed to send said network resolver a dummy ARP request upon power up or reset, to allow said network resolver to populate said address resolution table. 